Technical Abstract:
Manganese (Mn) is essential for normal brain function and behavior. There has been speculation that moderate Mn intoxication or deficiency may be associated with increases in aggressive behavior. Therefore, this study examined, under experimental conditions, the effect of dietary Mn excess or deprivation on aggression responses. Subjects: Thirty-six male, Long-Evans rats (aged 90-100 days). Diet: AIN93G diet containing 1, 10 or 100 ug Mn crossed with either 2500 or 5000 ug Ca /g diet, as carbonates. Design: Each of the experimental diets was fed to 6 rats each for 12 weeks, and a resident-intruder procedure was used to systematically assess and quantify aggressive, submissive and non-agonistic behaviors during a 5-minute recording session. Ultrasonic vocalizations consistent with aggressive (50 kHz) and submissive (25 kHz) behaviors were also recorded. Results: Rats fed diets containing deficient or excessive concentrations of Mn were generally less active than those fed adequate Mn. Consequently, these rats engaged in fewer aggressive behaviors (attacking, biting, wrestling, aggressive contact) and displacement activities (exploration, self-grooming), and more posturing. However, rats fed diets high in Mn but low in Ca showed some increased aggressive behavior compared to rats fed other diets. Conclusion: Findings provide weak support for earlier reports that Mn excess increases aggression, primarily because rats fed high Mn were less active than those fed adequate Mn. No support was found for the hypothesis that Mn deprivation is associated with increased aggression. Findings expand our knowledge of the functional role of dietary Mn, and its interaction with Ca, at physiological as well as toxicological concentrations.